Tuning indicator



June 12, 1951 G. c. szlKLAl ET AL TUNING INDICATOR Filed not. 15, 1945 n w n f M w m u S'nventor's e C .Szzklaz Patented June 12, 1951 TUNING INDICATOR George C. Sziklai, Princeton, N. J., and Robert R. Thalner, Reading, Mass., assignors to Radio Corporation of America, a corporation of Dela- Ware Application October 15, 1946, Serial No. 703,292

6 Claims.

This invention relates to devices for indicating resonance conditions and signal strength in radio circuits and is particularly useful for frequency modulated or FM signals. In tuning indicators heretofore used the indication has shown resonance conditions only. When a receiving set, for example, is new and the tuner and discriminator are correctlyV related, resonance indications would mean that maximum signals are being received but after the set has been in use the correct relation between tuner and discriminatorv is likely to be impaired and the resonance indicator cannot determine maximum signal.

' It is an object of this invention to provide an indicator that visually depicts both the correct tuning and the maximum signal.

Other objects of the invention will appear in the following specification with reference to the drawing in which: Fig. l is a diagrammatic illustration of the improved indicator tube;

Fig. 2 is a plan of the target used in the indicator with the fluorescent screen shown in section;

Fig. 3 contains graphs illustrating the voltagefrequency relation of the discriminator circuits; and

Fig. 4 is a diagrammatic illustration of rtuning and signal conditions.

.,Referring to Fig. 1 the indicator tube comprises an evacuated envelope I containing elements like those disclosed in the application of cof-inventor George C. Sziklai for a frequency modulation, or FM, detector, iled May 20, 1944, Serial No. 536,457, which issued as Patent Number 2,408,702, dated October l, 1946, with the exception that the target is so constructed as to project the cathode ray beam onto a fluorescent screen to provide an indication of tuning and signal strength conditions. Reference character 2 indicates a cathode for providing the electrons which are formed into a beam by anode 3 containing a suitable aperture to dene the beam and to accelerate it along the tube axis. One pair of oppositely disposed deection plates 4, 5 positioned at 90 to the vertical, as shown in Fig. 1, and another opposite pair 6, I positioned Vertically, are arranged in spaced relation around the beam. The plates 4, 5 are connected to the terminals of one circuit 8 of a frequency discriminator and the other pair 6, 1 are connected to the terminals of the circuit 9 thereof. These circuits comprise transformer coils coupled to a primary coil I0 connected to receive incoming signals, for

example, to the intermediate frequency circuit of a superheterodyne receiver of FM signals. One circuit, say 8, is tuned by the-condenser II to a frequency F2 somewhat above the upper limit of the signal modulation frequency (Fig. 3) and the other circuit is tuned by its condenser I2 to a 2 frequency FI somewhat below the lower limit of the signal modulation frequency Fc. The median frequency Fc is the intermediate carrier frequency ,around which the modulation frequencies center.

The ordinates of the graphs indicate voltage in Fig. 3. The Q of the circuits will be adjusted so that at frequency Fc the voltages Will be at quadrature.

At the end of the tube remote from the cathode 2V is positioned the uorescent screen I3. This may be coated on the end of the tube envelope or positioned therein in any other Way. In front of the screen is placed the target comprising a first pair of oppositely positioned conducting quarter sectors I5 and I6 which have good secondary emission properties so that their emission ratio is greater than unity. The target further comprises two conducting plates mounted behind the sectors I5 and I6 in insulated relation thereto, with sector portions Il, Il and I8, I 8 exposed to the beam on each side of the sectors I5 and I6, respectively. The plates are spaced from each other to form a slot I9 therebetween. The spaced sector portions I'I, I8 and I'I, I8 form two oppositely-disposed quarter sectors alternating with the quarter sectors I5 and I6 and bisected by the slot I9. The sectors I5 and I6 are conductively connected as by joining them at the center by a connecting web. Sectors I5 and I5 may have a surface such as caesiated silver oxide or silver magnesium alloy which copiously emits secondary electrons under beam bombardment so as to assume a position potential. The pair of sectors consisting of I'l, I8 and I'I, I8 may have a carbon surface which as well known is a poor secondary emitter.

Sectors I5 and I6 are connected to ground through resistance 2l and condenser 22 which constitute an integrating circuit for producing the detected signals, as in my said co-pending application, by the scansion of the beam over these sectors. For utilization of the signal the amplier, not shown, would be connected to lines L. The sector portions Il, I1 and I8, I8 are electrically connected to delecting plate 23, 24, respectively. Sector portions Il, Il" are connected by slider 25 with resistance 2l at or near its junction with condenser 22. Sector portions I8, I8 are connected to ground through adjustable bias source 26 either positive or negative.

Screen anode 2l which has a higher positive voltage than anode 3 accelerates the electrons to target T and collects secondary electrons emitted thereby.

The operation of our improved indicator may be described as follows:

With an unmodulated carrier Fc the voltages vapplied to the delecting plates 4, 5 and 6, 'l are in quadrature and a circle as at a (Fig. 4) is traced over the target. The beam passes through the slot i9 and produces two luminescent spots 28, 29 on the fluorescent screen i3. If the slot i9 is much wider than the diameter of the beam, the spots 28 and 29 will have the form of short arcs or lines. The secondary emission from sectors i5 and i8 makes these sectors go positive and the potential is integrated by resistance 2l and condenser 22 for production of an audio signal. The luminous area may be brought to the center line of the screen i3 by applying a biasing voltage to deflector 28 by source 26.

When the carrier Fc is frequency modulated the trace of the beam will be a right line b (Fig. Il) when frequency F2 is reached. The trace will change through an ellipse as at c, then a circle as at a at frequency Fc, then an ellipse d with its major axis at a right angle to that of ellipse c, and nnally at frequency FZ to a right line at e at a right angle to the line b. As the frequency modulation swings back through Fc to F2 the trace will go in the reverse direction from e to a. Thus, the modulation frequency will'cause the Vbeam to scan the target and pass vthrough slot E9 to produce a line on the screen linstead of two spots. receiving set tunes in a station, the carrier will appear as two spots if unmodulated and its strength will be indicated by the diametrical distance between them. If the carrier is modulated the solid line will widen in Fig. 1 to produce luminous rectangle B. This is due to the increased audio voltage applied to plate 23 by increased current in resistance 2l. The strength of the modulation is therefore indicated by the width of the luminous band and tuning of the set will be continued until maximum width is obtained. This maximum is produced by the tuning adjustinent even if the tuning be out of correct relation with the discriminator.

While certain specific embodiments have been illustrated and described, it will be understood vthat various changes and modifications may be made therein without departing from the spirit and scope of the invention.

What we claim as new is:

1. An electron discharge device, comprising an evacuated envelope containing a cathode and an anode adapted to form a cathode ray beam, a fluorescent screen in the path of the beam, a

planar target comprising four sectors positioned anode adapted to form a cathode ray beam, a

fluorescent screen in the path of the beam, a circular target between said screen and anode having four quarter sectors positioned to be scanned by said beam, one pair of opposite quarter sectors being electrically joined and having surfaces of high secondary electron emission properties, the other pair of sectors being bisected by a diametrical slot and having surfaces of low secondary electron emissive properties.

3. An electron discharge device, comprising an evacuated envelope containing a cathode and an anode adapted to form a cathode ray beam, a uorescent screen in the path of the beam, a planar target comprising four sectors positioned to be scanned by said beam, one pair of opposite Thus, as the user or" the lll iii)

sectors being electrically joined, and having surfaces of high secondary electron emission properties, the other pair of sectors being bisected by a slot and having surfaces of low secondary electron emission properties, field producing means for deflecting said beam along a diameter in one direction and field producing means for deecting said beam along a diameter in the direction normal to said one direction.

fi. An electron discharge device for frequency modulated waves, comprising an evacuated envelope containing a cathode and an anode adapted to form a cathode ray beam, a fluorescent screen in the path of the beam, a planar target comprising four sectors positioned to be scanned by said beam, one pair of opposite sectors being electrically joined, and having surfaces of high secondary electron emission properties, the other pair of sectors being bisected by a slot and having surfaces of low secondary electron emission properties, deflector plates joined to the halves of the second mentioned sectors at opposite sides of said slot.

5. A tuning indicator system for frequency modulated wavescomprising an evacuated envelope containing a cathode and an anode adapted to form a cathode ray beam, a iluorescent screen in the path of the beam, a planar target comprising four sectors positioned to be'scanned by said beam, one pair of opposite sectors vbeing electrically joined, and having surfaces of high secondary electron emission properties, the other pair of sectors being bisected by a slot and having surfaces of low secondary electron emission properties, eld producing means for deilecting said beam along a diameter normal to said slot and eld producing means for deecting said beam along a diameter normal to said first mentioned diameter, and an integrating circuit between the first mentioned sectors and said cathode.

6. A tuning indicator system for frequency modulated waves, comprising an evacuated envelope containing a cathode and an anode adapted to form a cathode ray beam, a fluorescent screen in the path of the beam, a planar target Ycomprising four sectors positioned to be scanned by said beam, one pair of opposite sectors being electrically joined, and having surfaces of high secondary electron emissiony properties, the other pair of sectors being bisected by a slot and having surfaces of low secondary electron emission prop,- erties, neldproducing means for deflecting said beam along a diameter in oneV direction and eld producing means for deflecting said beam along a diameter normal to said first mentioned diameter, an integrating circuit connected between the said one pair of sectors and said cathode,.the sector portions at one side of said slot being connected to an intermediate part of said circuit and the sector portions at the other side of the slot being connected to a positive source of .potential relative to the cathode.

GEORGEv C. SZIKLAI. ROBERT R. THALNER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,051,188 Thompson Aug. 18, 1936 2,178,238 Massa et al Oct. 1l, 1939 

